1. Field of the Invention
The present invention relates to a pulley unit.
2. Description of the Related Art
Heretofore, there has been known a pulley unit including a one-way clutch and mounted on a rotational shaft of an accessory which is driven by a crankshaft of an engine through a belt in an automobile or the like. Examples of such an accessary include compressors for air conditioners, water pumps, alternators, cooling fans and the like in automobiles. The pulley unit includes a sleeve. The sleeve has a cylindrical shape. The sleeve includes on one side in an axial direction a first opening end portion for insertion of an end portion of a rotational shaft. The sleeve also includes a second opening end portion provided on a side that is opposite from the first opening end portion and having, as an inner periphery, a polygonal inner peripheral portion with a polygonal cross-section. The pulley unit also includes a pulley that is arranged concentrically on a radially outer side of the sleeve to be supported rotatably about the axis of the sleeve, and has an outer peripheral surface on which a belt is wound. The pulley unit also includes a cap member that has a cover portion covering the second opening end portion and claw portions engaged with a stepped attaching portion provided on an inner surface of the sleeve. In the pulley unit, a rotational shaft of an automotive accessory (rotor shaft of an alternator, for example) is inserted into the sleeve on the first opening end portion side, and a mounting jig is fitted in the polygonal inner peripheral portion at the second opening end portion of the sleeve, whereby the pulley unit is fastened and fixed on the rotational shaft (refer to Japanese Patent Application Publication No. 2003-232434 (JP 2003-232434 A) for example).
Such a pulley unit may be arranged at a place in the accessory, which is prone to be splashed with mud water or the like. Thus, the end surface, the inner surface and the like at the second opening end portion of the sleeve are prone to rust. It is generally conceived to give such exposed metal portions a rust prevention treatment. However, for fastening and fixing the pulley unit on a rotational shaft, it is stipulated to perform the tightening with a predetermined tightening torque. It is expected that when the tightening on the rotational shaft is carried out with the inner surface of the sleeve having been provided with coating in the rust prevention treatment, the tightening and fixing with a standard tightening torque becomes difficult. Therefore, in fixing the pulley unit on the rotational shaft of the accessory, the pulley unit is mounted without performing the rust prevention treatment on the sleeve and then, the second opening end portion is covered with the cap member. In the cap member in the aforementioned JP 2003-232434 A, a plurality of claw portions that are engaged with a stepped attaching portion on the inner surface of the sleeve are provided so as to extend from the cover portion covering the second opening end portion.
However, in the cap member in the aforementioned JP 2003-232434 A, because the claw portions are provided separate from one another in the circumferential direction, gaps are formed at respective root parts of the claw portions. Therefore, there is a possibility that mud water entering from an end surface of the sleeve easily enters the interior of the sleeve through the gaps. For this reason, a further improvement has been desired for reducing the entry of water in the cap member.